1. Field of the Invention
The present invention relates to an image forming apparatus and a method of manufacturing and adjusting the same and, more particularly, to an image forming apparatus using a multi-electron-beam source in which a plurality of surface conduction electron-emitting devices are arranged, and a method of manufacturing and adjusting the same.
2. Related Background Art
Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Examples of cold cathode devices are field emission type emission devices (to be referred to as FE type devices hereinafter), metal/insulator/metal type emission devices (to be referred to as MIM type devices hereinafter), and surface conduction electron-emitting devices.
Known examples of the FE type devices are described in W. P. Dyke and W. W. Dolan, "Field emission", Advance in Electron Physics, 8,89 (1956) and C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47,5248 (1976).
A known example of the MIM type devices is described in C. A. Mead, "Operation of Tunnel-emission Devices", J. Appl. Phys., 32,646 (1961).
A known example of the surface conduction electron-emitting devices is described in, e.g., M. I. Elinson, Radio. Eng. Electron Phys., 10 (1965) and other examples to be described later.
The surface conduction electron-emitting device utilizes the phenomenon that electron emission is caused in a small-area thin film, formed on a substrate, by passing a current parallel to the film surface. The surface conduction electron-emitting device includes devices using an Au thin film (G. Dittmer, "Thin Solid Films", 9,317 (1972)), an In.sub.2 O.sub.3 /SnO.sub.2 thin film (M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975)), and a carbon thin film (Hisashi Araki, et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983)), and the like, in addition to an SnO.sub.2 thin film according to Elinson mentioned above.
FIG. 24 is a plan view of the surface conduction electron-emitting device according to M. Hartwell et al. as a typical example of the structures of these surface conduction electron-emitting devices. Referring to FIG. 24, reference numeral 3001 denotes a substrate, and 3004 a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 24. An electron-emitting portion 3005 is formed by performing an electrification process (referred to as an energization forming process to be described later) with respect to the conductive thin film 3004. Referring to FIG. 24, a spacing L is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion 3005.
In the above surface conduction electron-emitting device by M. Hartwell et al., typically the electron-emitting portion 3005 is formed by performing the electrification process called the energization forming process for the conductive thin film 3004 before electron emission. According to the energization forming process, electrification is performed by applying a constant DC voltage which increases at a very slow rate of, e.g., 1 V/min, to both ends of the conductive thin film 3004, so as to partially destroy or deform the conductive thin film 3004 or by changing the properties of the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 or the part where the properties are changed has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the energization forming process, electron emission is performed near the fissure.
The above surface conduction electron-emitting devices are advantageous because they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface conduction electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, charged beam sources and the like have been studied.
As an application to image display apparatuses, in particular, as disclosed in U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open No. 2-257551 filed by the present applicant, an image display apparatus using the combination of a surface conduction electron-emitting device and a phosphor which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus is expected to have better characteristics than other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight since it is of a light emissive type and that it has a wide view angle.
The present inventors have examined surface conduction electron-emitting devices according to various materials, manufacturing methods, and structures, in addition to the above conventional devices. The present inventors have also studied a multi-electron-beam source in which a lot of surface conduction electron-emitting devices are arranged and an image display apparatus to which this multi-electron source is applied.
The present inventors have also examined a multi-electron-beam source according to an electric wiring method shown in FIG. 25. More specifically, this multi-electron source is constituted by two-dimensionally arranging a large number of surface conduction electron-emitting devices and wiring these devices in a matrix, as shown in FIG. 25.
Referring to FIG. 25, reference numeral 4001 denotes a surface conduction electron-emitting device, 4002 a row wiring layer, and 4003 a column wiring layer. The row wiring layers 4002 and the column wiring layers 4003 actually have limited electrical resistances which are represented as wiring resistances 4004 and 4005 in FIG. 25. The wiring shown in FIG. 25 is referred to as simple matrix wiring.
For illustrative convenience, the multi-electron source constituted by a 6.times.6 matrix is shown in FIG. 25. However, the scale of the matrix is not limited to this arrangement, as a matter of course. In case of a multi-electron-beam source for an image display apparatus, a number of devices sufficient to perform desired image display are arranged and wired.
In the multi-electron source in which the surface conduction electron-emitting devices are wired in a simple matrix, as shown in FIG. 25, appropriate electrical signals are supplied to the row wiring layers 4002 and the column wiring layers 4003 to output desired electron beams. When the surface conduction electron-emitting devices of an arbitrary row of the matrix are to be driven, a selection voltage Vs is applied to the row wiring layer 4002 of the selected row. Simultaneously, a non-selection voltage Vns is applied to the row wiring layers 4002 of unselected rows. In synchronism with this operation, a driving voltage Ve for outputting electron beams is applied to the column wiring layers 4003. According to this method, a voltage (Ve-Vs) is applied to the surface conduction electron-emitting devices of the selected row, and a voltage (Ve-Vns) is applied to the surface conduction electron-emitting devices of the unselected rows, assuming that a voltage drop caused by the wiring resistances 4004 and 4005 is negligible. When the voltages Ve, Vs, and Vns are set to appropriate levels, electron beams with a desired intensity are output from only the surface conduction electron-emitting devices of the selected row. When different driving voltages Ve are applied to the respective column wiring layers, electron beams with different intensities are output from the respective surface conduction electron-emitting devices of the selected rows. Since the response of the surface conduction electron-emitting device is very quick, the period of time over which electron beams are output can also be changed in accordance with the period of time for applying the driving voltage Ve.
The multi-electron source having surface conduction electron-emitting devices arranged in a simple matrix can be used in a variety of applications. For example, the multi-electron source can be suitably used for an image display apparatus by appropriately supplying an electrical signal according to image information.
However, the multi-electron source in which the surface conduction electron-emitting devices are arranged in the simple matrix has the following problem in fact.
As described above, when an image display apparatus is constituted by combining surface conduction electron-emitting devices and phosphors which emit light upon irradiation of electron beams, phosphors of three primary colors, i.e., red (R), green (G), and blue (B) are normally used.
However, since the R, G, and B phosphors exhibit different light emission characteristics, as will be described later, no satisfactory white balance can be obtained when electron beams having the same intensity are incident on the phosphors of the respective colors.
FIG. 26A is a graph showing typical light emission characteristics of the phosphors of the respective colors. As shown in FIG. 26A, the characteristic curve of a phosphor changes depending on the color of emitted light and has non-linearity. The light emission characteristic of a phosphor is defined depending on the total amount of charges reaching a unit-area phosphor surface per unit time. The degree of non-linearity also changes depending on the type of the phosphor.
The non-linearity of the characteristic curve of the phosphor can be corrected to an almost linear characteristic by inserting, for each color, a gamma correction circuit which is conventionally used for a CRT or the like. FIG. 26B is a graph showing the characteristics of the respective color phosphors after gamma correction. The gradient changes depending on the colors. When the difference between the gradients according to the colors does not correspond to the ratio of incident electron beam intensities for the respective colors, which ratio defines a satisfactory white balance, the color reproduction properties are degraded.